WO2014044515A1

WO2014044515A1 - Method for producing a circuit board element, and circuit board element

Info

Publication number: WO2014044515A1
Application number: PCT/EP2013/067988
Authority: WO
Inventors: Markus WÖLFEL
Original assignee: Jumatech Gmbh
Priority date: 2012-09-20
Filing date: 2013-08-30
Publication date: 2014-03-27
Also published as: JP2015529402A; US20150237738A1; DE102012216926A1; EP2898759A1; EP2898759B1; CN104756613A; JP6067859B2; CN104756613B

Abstract

The present invention relates to a method for producing a circuit board element and to a corresponding circuit board element with which it is possible to suppress the risk of delamination in the region of a component (e.g. a wire or a plate-shaped moulded part) that is embedded in the circuit board. To this end, according to the invention the surface of the component is at least partially roughened, in order to ensure a better adhesive bond with the surrounding cover layer (e. g. a prepreg made of insulating material compound). The component surface can be roughened by chemical methods such as etching or by purely mechanical methods such as sand blasting.

Description

Method for producing a printed circuit board element

and PCB element

The invention relates to a method for producing a printed circuit board element, in which initially a component made of an electrically conductive material and this component is contacted with an electrically conductive film at least one contact point, before subsequently a cover layer is applied to the component contacting side of the film ,

Furthermore, the invention relates to a printed circuit board element having at least one electrically conductive film, with a cover layer which covers the film on at least one side, and with at least one component made of an electrically conductive material, wherein the component at least one contact point with the film in Contact is and at least partially, preferably completely, embedded in the cover layer.

The trend towards smaller and more powerful electronic devices, such as smartphones and tablets, has been leading to increasing integration density on printed circuit boards for years.

A clear advantage in this respect show wire-printed circuit boards, in which lead wires are applied to the top and / or bottom of a copper foil. After pressing the film with an electrically insulating cover layer, usually a prepreg of an epoxy resin fiberglass fabric, the wires are inside the laminate, embedded in the prepreg.

By means of this wire writing technique described, for example, in WO 2008/055672 A1, three-dimensional circuit geometries for extreme packing densities can be realized in printed circuit boards. Although this overcomes many technical limitations of conventional printed circuit board technology, wire-printed circuit boards can still be improved with regard to their delamination resistance.

The delamination of PCB elements is a serious challenge, especially since multilayer printed circuit boards (multilayer) are exposed to ever-increasing thermal and / or mechanical stresses. The adhesion values between the individual layers of the multilayer, ie between the individual copper foils and the respectively interposed prepreg layers (epoxy resin fiberglass fabric layers), could be improved in recent years by an upstream treatment of the surface of the copper foils with chemical agents ("brown oxide"). - or "black oxide" treatment) and significantly increased by the use of improved epoxy resin blends for prepregs.

However, the incorporation of additional components into the prepreg layers of the printed circuit board leads to an increase in the risk of delamination, since the delamination is due first to the "weak points" between the surfaces of the embedded components and the surrounding prepreg and not to the much stronger bond between the treated copper foil surface and the prepreg noticeable.

Particularly in wire-printed circuit boards, weakening of the adhesive bond takes place through the lead wires embedded in the prepreg.

This problem is compounded by the fact that the additionally introduced into the interior of the circuit board wires can be designed as silver-plated copper wires. Admittedly, the silver layer galvanically applied to the copper core not only has a very good conductivity, but in particular is also very readily weldable. In addition to the economic disadvantages (silver-plated copper wires are many times more expensive than pure copper wires), however, the silver layer due to their relatively smooth surface only a very poor adhesion to the surrounding layer of prepreg.

Accordingly, it is an object of the present invention to provide a method for producing a printed circuit board element or a printed circuit board element, which allows excellent adhesion between the additionally integrated in the PCB element components and their respective surrounding cover layer, so that no delamination of the printed circuit board element in the region of the cover layer embedded components takes place.

This object is achieved according to claim 1 by a method for producing a printed circuit board element in which the surface of the component is at least partially roughened before applying the cover layer, so that when applying the cover layer to the film, the cover layer with the roughened surface of the device in contact is brought. By virtue of the component embedded in the printed circuit board element having an at least partially roughened surface instead of a comparatively smooth surface, for example instead of a smooth silver metal surface, a significantly better adhesion is ensured between the component and the covering layer surrounding the component. Thus, components can be easily integrated into a multilayer, without starting from a detachment of the device from the adjacent cover layer to delamination of the circuit board. Thus, for printed circuit boards with embedded components (including in the form of wire-printed circuit boards) open up new applications, which previously appeared to be hardly feasible due to their extreme environmental conditions, for example, the use in high-temperature applications, for example in automotive electronics.

Preferably, in the method according to the invention, the roughening of the surface of the component takes place prior to contacting the component with the foil. The roughened component surface has no negative influence on the quality of the contact between the component and the foil (for example by resistance welding) to be produced so that with little effort and high, continuous throughput, the entire surface of the components of an upstream roughening treatment can be subjected.

In particular, the roughening of the surface of the device can be realized by chemical etching, wherein the chemical etching is preferably carried out by immersing the device in a liquid etching the material of the device or by spraying the device with such a liquid. Before the actual microetching process, the components to be treated are cleaned and their metal surfaces are degreased by an acidic or alkaline solution (cleaner). After the micro-etching process, which can be carried out, for example, in a flood module with splash nozzles (bond), residual residues of the etching liquid are removed in a cascade rinsing module before the components are finally dried without staining.

Alternatively, the surface of the device can also be roughened by mechanical processing, for example by sandblasting or by the spraying of pumice or quartz powder under high pressure, thus making it more adhesive. Mechanical roughening methods have the advantage that the surface roughness is produced solely by mechanical removal, so that it is possible to dispense with the use of aggressive etching solutions, which are expensive to purchase and to dispose of. In a further preferred manner, the application of a cover layer to the component contacting side of the film by pressing the side of the film is carried out with a prepreg of insulating material. The pressing is done in such a way that the stocked with the component copper foil and the prepreg (epoxy glass fiber fabric blank) is introduced into a laminate press and ejected after pressure and heat as pressed final product the circuit board element, which with the established processes (etching process of au Shen and equipping with SMD components) can be completed.

Preferably, a plurality of electrically conductive films, of which at least one is contacted with at least one component made of an electrically conductive material, and a plurality of inserted respectively between the films prepreg of insulating material pressed together to form a multilayer printed circuit board element. In particular, in such a compression to the multilayer sufficient interlaminar adhesion must be ensured between each layer position, since even individual local lifts, as can be caused by prepreg embedded components, can lead to delamination and thus total failure of the multilayer PCB element.

The object underlying the invention is also achieved according to claim 8 by a printed circuit board element of the type mentioned, in which at least a part of the surface of the cover layer in contact surface of the device is roughened. The micro-fine roughening of the component surface results in the ideal surface topography for the optimum adhesion of the component and the surrounding cover layer, so that the risk of delamination of the printed circuit board element emanating from the embedded component can be virtually ruled out.

In the on the film to be pressed, in particular copper foil, applied component may in particular be a lead wire, in particular copper wire, which is arranged after pressing in the interior of the printed circuit board element and contacted via etched pads from the outside (so-called wire printed circuit boards) ,

However, the component can also be embodied as a plate-shaped molded part extending in the printed circuit board element, in particular as a copper shaped part, whereby for example the required line cross-sections for mastering by means of such a molded part the occurring in the field of power electronics currents and heat quantities can be provided with little effort.

The invention will now be explained below with reference to two figures. They show in detail:

FIG. 1a shows a schematic cross-sectional view of the layers of a multi-layer printed circuit board element according to the invention, as they lie on one another in the unpressed state,

Figure 1 b is a schematic cross-sectional view of a multilayer printed circuit board element according to the invention in the compressed state.

FIGS. 1 a and 1 b show, in cross-sectional view, the individual material layers of a printed circuit board element 1 according to the invention for better differentiation with another surface filling. With each oblique hatching, the components 2, 3 are shown, which are embedded in the printed circuit board element 1. With dark solid tone, the copper foils 4 are shown, while in bright solid color, the epoxy glass fiber fabric layers 5, hereinafter generally called prepreg, can be seen in cross section.

The components, which are on the one hand to three circular cylindrical copper wires 2 and the other to a plate-shaped copper molding 3, z. B. in the form of a copper flat wire is, have been fixed in an upstream process step respectively on the side 4a, 4b of a copper foil 4. This process step of fixing the components 2, 3 to the copper foils 4, which is not shown in the figures, is carried out by means of a numerically controlled device for material-locking connection, which is preferably carried out at defined contact points by means of resistance spot welding. The wires 2 are actively tracked, held down in a defined desired position, cut and welded by means of a likewise controlled movable welding electrode.

As a molded part 3 in the sense of this invention, a component is preferably referred to, which is produced in a separation process in which the shape of a workpiece is changed, wherein the molded part 3 is separated from the workpiece and the final shape is contained in the initial shape. In Figures 1 a and 1 b, the upper copper foil 4 is provided on its underside 4 a with a herausgeschennten from a copper plate, plate-shaped part 3, wherein copper foil 4 and molded part 3 also at precisely defined connection points a cohesive bonding method, such as by resistance spot welding, have been contacted with each other.

FIG. 1 a shows the cross-sectional view of an intermediate product in the method for producing the multilayer printed circuit board element 1 according to the invention. This intermediate product shows the structure of a layer stack 6 of a plurality of superimposed electrically insulating layers of prepreg 5 and a plurality of conductive layers of copper foil 4, these layers have been shown only for better illustration with a vertical distance from each other. Two of the copper foils 4 have been equipped on a side 4a, 4b with additional components (wires 2 or molded part 3) according to the pre-formed method step, wherein these two copper foils 4 are oriented in the layer stack 6 so that the component 2, 3 contacting film side 4a, 4b points into the interior of the layer stack 6, so that the components 2, 3 always come to lie in the interior of the printed circuit board element 1 after being pressed.

According to FIG. 1 a, the layer stack 6 described above is introduced between the press plates 7 a, 7 b of a laminate press, wherein a pressure (see arrows directed towards one another in FIGS. 1 a and 1 b) by means of the press plates 7 a, 7 b on the At the same time the temperature of the layers to be laminated is increased to a desired temperature above the room temperature to be laminated together layers of the printed circuit board element 1.

It should be noted that the pressing process illustrated by the transition from FIG. 1 a to FIG. 1 b has been reproduced in a highly simplified manner. The production of a multilayer printed circuit board element 1 takes place in practice namely by means of a multi-stage process. Accordingly, first the middle layers of the layer stack 6 are pressed with layers of prepreg 5 placed between a lower and an upper copper foil 4 to form an intermediate product. Then, the outer copper foils 4 of this intermediate are first etched in a known manner from the outside. On the etched copper foils 4 more layers of prepreg 5 and final copper foils 4 are applied. This stack, not shown, already pressed intermediate product and additional externa ßeren layers is finally pressed to the finished multilayer printed circuit board element 1.

The inserted between each of the copper foils 4 prepreg 5 consists of an epoxy resin impregnated glass fiber fabric as Isolierstoffmasse that is plasticized under the pressure and heat described above and the subsequent curing a Bonding with the adjacent copper foils 4 causes. The plate-shaped molded part 3 attached to the underside 4 a of the upper copper foil 4 is embedded in the insulating material of the prepreg 5 during pressing in such a way that all sides of the molded part 3 are covered over its entire surface with the insulating material of the prepreg 5. However, provided between the molding 3 and copper foil 4, at least one contact point is not enclosed by the prepreg 5. The circular cylindrical conductor wires 2 are also almost completely embedded in the insulating material of the prepreg 5 during pressing. Again, the at least one contact point between the respective wire 2 and the copper foil 4 is not covered by the prepreg 5 alone.

For a better adhesion between prepreg 5 and copper foil 4, it is known to pretreat the surfaces of the copper foils 4 by an oxidation process ("brown oxide" or "black oxide"), so that during the subsequent compression according to FIG. 1 b to the multilayer printed circuit board element 1 a better one Adhesive bond between the copper foils 4 and the insulating cover layers 5 (prepregs) can be ensured. However, the printed circuit board element 1 constructed in accordance with the present invention has particular challenges with regard to the delamination resistance, since a weakening of the adhesive bond of the printed circuit board element 1 occurs due to the additionally embedded in the insulating material of the prepreg 5 components 2, 3. In contrast to the copper foil surfaces, the device surfaces 2o, 3o have only a very weak adhesion to the respectively adjacent prepreg 5.

The reason for this is, inter alia, that in wire-printed circuit boards (that is to say printed circuit boards whose copper foils 4 are welded to wires 2), in most cases galvanically silver-plated copper wires are used as embedded components. Although the outer silver layer of these wires has very good welding properties for achieving a secure bond with the copper foil 4, the adhesion of the silver layer to the surrounding prepreg 5 is insufficient due to the rather smooth surface of the silver layer. As a consequence, local lifting off of the silver layer of the component from the surrounding prepreg 5 may occur, which in extreme cases may become the starting point for complete delamination and thus total failure of the printed circuit board element 1.

Here, the present invention addresses and overcomes the problem of poor adhesion of embedded device 2, 3 and surrounding layer of prepreg 5 in that the surface 2o, 3o of the device 2, 3 in contact with the prepreg 5 "Roughened" here means that the surface 2o, 3o of the component 2, 3 before the application of the cover layer 5 on the copper foil 4 and the case thereby embedding the component 2, 3 in this cover layer 5 of a targeted Aufaufaut Since this micro-roughness has no significant effect on the quality of the welded joints between components 2, 3 and copper foils 4, the components 2, 3 can already be used in their semi-finished state Wire or sheet goods are pretreated with low expenditure in high throughput speed before they are fed to the actual circuit board manufacturing process.

The roughening treatment can be a chemical roughening in which the component surface 2o, 3o is contacted with a corrosive solution in a multistage dipping and / or spraying process and the surface material is partially etched away, or can be a mechanical roughening, wherein the component surface 2o , 3o mechanical forces is subjected.

The chemical roughening is advantageously carried out in multi-stage systems with several modules connected in series, wherein the surfaces 2o, 3o of the continuously guided through the system components 2, 3 before the actual microetching usually cleaned, rinsed and pre-immersed and after the micro-etching process rinsing again takes place to remove the corrosive solution residues. The mechanical roughening can be produced, for example, by using a dense mass of minute spheres of, for example, steel, glass, pumice, quartz powder or the like, or by brush roughening techniques. It would also be conceivable to achieve the roughening by introducing a simple profiling (for example of notches) into the component surface 2o, 3o.

The roughened surface 2o, 3o of the component 2, 3 gives the component 2, 3 contacting layer of the prepreg 5 after pressing and curing a corresponding roughness, which is complementary to the roughness of the device surface 2o, 3o formed. The interlocking of the intermeshed roughness peaks of device surface 2o, 3o and adjacent layer of prepreg 5 explains the excellent adhesion of device 2, 3 and prepreg 5.

As a result of the improvement according to the invention, components 2, 3 can be integrated into the inner layers of printed circuit board elements 1 without problems, without fear of delamination or cracking and thus functional failures of the printed circuit board element 1 have to. This is especially true for high temperature applications, such as automotive electronics or solar technology, where the connection between the surface 2o, 3o of the embedded device 2, 3 and the surrounding prepreg 5 is exposed to recurring heavy loads due to the different thermal expansion coefficients of both materials.

The present invention thus contributes, on the one hand, to a further increase in the integration density of components 2, 3 in printed circuit board elements 1 and, on the other hand, increases the range of use of such printed circuit board elements 1 up to high-temperature applications.

Claims

claims

1 . Method for producing a printed circuit board element (1), comprising the following steps: a) providing a component (2, 3) made of an electrically conductive material, b) contacting the component (2, 3) with an electrically conductive foil (4) at least a contact point, c) applying a cover layer (5) to the component (2, 3) contacting side (4a, 4b) of the film (4), characterized in that the surface (2o, 3o) of the component (2, 3 ) is at least partially roughened before step c) and the cover layer (5) in step c) with the roughened surface (2o, 3o) of the device (2, 3) is brought into contact.

2. The method according to claim 1, characterized in that the roughening of the surface (2o, 3o) of the device (2, 3) before contacting the device (2, 3) with the film (4) according to step b).

3. The method according to claim 1 or 2, characterized in that the surface (2o, 3o) of the device (2, 3) is roughened by chemical etching, wherein the chemical etching preferably by immersing the device (2, 3) in a the Material of the component (2, 3) corrosive liquid or by spraying the device (2, 3) is carried out with such a liquid.

4. The method according to claim 1 or 2, characterized in that the surface (2o, 3o) of the component (2, 3) by mechanical processing, for example by sandblasting or by spraying pumice or quartz flour under high pressure, roughened.

5. The method according to any one of claims 1 to 4, characterized in that the contacting of the component (2, 3) with the film (4) according to step b) by welding, preferably by resistance welding takes place.

6. The method according to any one of claims 1 to 5, characterized in that the application of a cover layer (5) on the component (2, 3) contacting side (4a, 4b) of the film (4) according to step c) by pressing the Side (4a, 4b) of the film (4) with a prepreg (5) made of insulating material.

7. The method according to claim 6, characterized in that in step c) a plurality of electrically conductive films (4), of which at least one with at least one component (2, 3) made of an electrically conductive material is contacted, and a plurality of each inserted between the films prepregs (5) made of insulating material are pressed together to a multi-layer printed circuit board element (1).

8. printed circuit board element comprising

at least one electrically conductive foil (4),

at least one covering layer (5) which covers the film (4) on at least one side (4a, 4b),

- At least one component (2, 3) made of an electrically conductive material, wherein the component (2, 3) at least one contact point with the film (4) in contact and at least partially, preferably completely, embedded in the cover layer (5) characterized in that at least a part of the surface (2o, 3o) of the component (2, 3) which is in contact with the cover layer (5) is roughened.

9. printed circuit board element according to claim 8, characterized in that the component is designed as preferably made of copper conductor wire (2) with a circular or rectangular cross-section.

10. printed circuit board element according to claim 8, characterized in that the component is formed as preferably made of copper, plate-shaped molding (3).